The work of recent years on uric acid metabolism has completely set aside the theory once universally accepted that in mammals uric acid is a product of the metabolism of all proteids, and an intermediary product in the formation of the end product urea. The acceptance of this theory rested on the comparison of proteid metabolism in mammals with that in birds and reptiles, and on the apparent parallelism between the excretion of uric acid and urea. In 1887 Mares1 studied the hourly excretion of uric acid and urea after rich proteid meals, and found that the uric acid excretion reaches its maximum and returns to a permanent level four or five hours before the urea reaches its maximum. Evidence has gradually accumulated to show that uric acid is an intermediary product of a group of proteids which form only a small part of the total proteid material of the